CVE-2020-35906: futures_task :waker May Cause A Use-after-free Vulnerability

HIGH
Advisory Identifier: GHSA-r93v-9p5q-vhpf
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CVSS 7.8
CWE-416
Published
Advisory Summary

CVE-2020-35906 is a HIGH (CVSS 7.8) :waker may cause a use-after-free vulnerability (CWE-416: Use After Free) affecting futures_task libraries in the crates.io ecosystem. The issue involves :waker may cause a use-after-free if used on a type that isn't 'static. Remediation is available by upgrading affected packages to version 0.3.6.

CVE-2020-35906 at a Glance

CVE Identifier CVE-2020-35906
GHSA Identifier GHSA-r93v-9p5q-vhpf
Severity HIGH
CVSS v3.1 Base Score 7.8
CWE Classification CWE-416: Use After Free
Affected Product futures_task
Package Ecosystem crates.io
Published Date
Last Updated

Security Impact

CVSS: 7.8

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H).

Attack Vector Local (AV:L)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2020-35906

To remediate this vulnerability, upgrade all affected futures_task dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

futures-task fixed: 0.3.6 
Upgrade futures-task to 0.3.6
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for futures-task

How to Check if You Are Affected

To determine whether your application is affected by CVE-2020-35906, inspect your project dependencies for futures_task:

inspect dependencies for futures-task

Analyze the terminal output to locate any version of futures_task in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.3.6), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-416: Use After Free, where the product reuses or references memory after it has been freed. at some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer. In futures_task, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

Affected versions of the crate did not properly implement a 'static lifetime bound on the waker function. This resulted in a use-after-free if Waker::wake() is called after original data had been dropped. The flaw was corrected by adding 'static lifetime bound to the data waker takes.

CVE-2020-35906 Affected futures_task Versions

1 component(s)
Fixed Versions:
0.3.6
Product / Package Ecosystem Affected Versions Fixed Version
futures-task
 crates.io
≥ 0.2.1
< 0.3.6
0.3.6

References

NVD — CVE-2020-35906 NVD
https://nvd.nist.gov/vuln/detail/CVE-2020-35906
futures_task Source Repository REPOSITORY
https://github.com/rust-lang/futures-rs/pull/2206
futures_task Source Repository REPOSITORY
https://github.com/rust-lang/futures-rs
rustsec.org/advisories/rustsec-... WEB
https://rustsec.org/advisories/RUSTSEC-2020-0060.html

Frequently Asked Questions

What is CVE-2020-35906?
CVE-2020-35906 is a security vulnerability in futures_task involving :waker may cause a use-after-free if used on a type that isn't 'static under CWE-416: Use After Free.
Which futures_task versions are affected?
Affected versions include releases prior to 0.3.6 across affected packages: futures-task.
What version fixes CVE-2020-35906?
Upgrading to 0.3.6 (or the latest patched release for your respective branch) resolves the vulnerability.
Is futures-task affected?
Yes, futures-task is affected in releases prior to 0.3.6. Upgrade your dependency to 0.3.6 or later.
What is the CVSS score of CVE-2020-35906?
CVE-2020-35906 has a CVSS v3.1 base score of 7.8 (HIGH) with vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2020-35906?
CVE-2020-35906 is classified under CWE-416: Use After Free (The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.).
How can I check crates.io dependencies for CVE-2020-35906?
Run the dependency tree command: 'inspect dependencies for futures-task'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-r93v-9p5q-vhpf",
  "modified" : "2025-10-30T19:53:41Z",
  "published" : "2022-05-24T17:37:49Z",
  "aliases" : [ "CVE-2020-35906" ],
  "summary" : "futures_task::waker may cause a use-after-free if used on a type that isn't 'static",
  "details" : "Affected versions of the crate did not properly implement a 'static lifetime bound on the waker function. This resulted in a use-after-free if Waker::wake() is called after original data had been dropped.\n\nThe flaw was corrected by adding 'static lifetime bound to the data waker takes.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "futures-task"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.2.1"
      }, {
        "fixed" : "0.3.6"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2020-35906"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rust-lang/futures-rs/pull/2206"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/rust-lang/futures-rs"
  }, {
    "type" : "WEB",
    "url" : "https://rustsec.org/advisories/RUSTSEC-2020-0060.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-416" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2022-06-16T23:58:42Z",
    "nvd_published_at" : "2020-12-31T09:15:00Z"
  }
}